An ion exchange resin for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene.

Imágenes(5)

Reclamaciones(17)

What is claimed is:

1. A method of separating a metal cation from an aqueous solution comprising contacting the aqueous solution with a polymeric ion exchange resin comprising a vinylidene diphosphonic acid component and an acrylic acid component.

2. The method of claim 1 wherein the polymeric exchange resin further comprises a styrene component.

4. The method of claim 1 wherein the diphosphonic acid component and the acrylic acid component are provided by hydrolyzing a copolymer comprising a vinylidene diphosphonic acid ester and acrylonitrile.

5. The method of claim 1 wherein the metal cation is uranium (VI) and the aqueous solution has a pH of about 2 to about 9.

6. The method of claim 1 wherein the aqueous solution is acidic.

7. The method of claim 6 wherein the metal cation is selected from the group consisting of an actinide in the III, IV or V oxidation state, and mixtures thereof.

8. The method of claim 7 wherein the actinide is selected from the group consisting of thorium, uranium, plutonium, americium and mixtures thereof, and the aqueous solution has a pH of about 2 or less.

9. The method of claim 6 wherein the metal cation is selected from the group consisting of a lanthanide in the (III) or (IV) oxidation state, and mixtures thereof.

10. The method of claim 6 wherein the metal cation is selected from the group consisting of yttrium(III), scandium(III), titanium(IV), zirconium(IV), hafnium(IV), and mixtures thereof.

11. A method of separating iron(III) from a complexing agent comprising contacting an iron(III) complex with a polymeric exchange resin comprising a vinylidene diphosphonic acid component and an acrylic acid component.

16. A method of separating a first monosaccharide from a second monosaccharide in an aqueous solution comprising contacting the aqueous solution with a polymeric exchange resin having a vinylidene diphosphonic acid component and an acrylic acid component.

17. The method of claim 16 wherein the first monosaccharide is selected from the group consisting of a fructose, galactose, mannose, and mixtures thereof, and the second monosaccharide is glucose.

Descripción

This invention was made with Government support under Contract No. W-31-109-ENG-38 awarded by the Department of Energy. The Government has certain rights in this invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 07/811,098 filed Dec. 20, 1991, now U.S. Pat. No. 5,281,631.

BACKGROUND OF THE INVENTION

The present invention is directed generally to a strong metal complexing resin for ion exchange columns. More particularly, the invention is related to an ion exchange resin prepared by copolymerizing diphosphonic acid groups with acrylonitrile, styrene and/or divinylbenzene to form a polymeric resin for preferentially removing heavy metal contaminants in a highly acidic solution.

A variety of far reaching environmental protection statutes and regulations have significantly increased the need for effective and efficient means for removal of a wide spectrum of metal contaminants from aqueous based wastes or contaminated waterways. In addition, specific industries, such as the nuclear industry and electroplating industry, generate substantial quantities of water based effluent which are heavily contaminated with undesirable metal ions. The removal of metal ion contaminantes from waste streams is often made difficult due to the strongly acidic nature of the waste effluent. Under such acidic conditions prior art metal complexing resins perform poorly to remove or recover such metals or have selectivity for only a very few types of metal ions. While phosphonic acids have been known to have the ability to complex with metal ions generally, there has been no demonstrated ability to allow selective removal of the chelated metal ions which is essential for selectivity of metal ion type as well as removal from the ion exchange resin.

It is therefore an object of the invention to provide an improved metal complexing resin for ion exchange columns.

It is also an object of the invention to provide a novel metal complexing resin and method of manufacture from copolymerization of diphosphonic acid groups with acrylonitrile, styrene and/or divinylbenzene.

It is an additional object of the invention to provide an improved method of preferentially removing toxic metal ions relative to alkaline and alkaline earth ions from strongly acidic water based wastes.

It is a further object of the invention to provide a novel product and method of manufacture of a sulfonated copolymer of diphosphonic acid group with acrylnitrile and styrene and/or divinylbenzene.

It is another object of the invention to provide an improved method of manufacturing a desired end product resin of narrow size distribution and uniform shape.

It is yet an additional object of the invention to provide a novel variety of copolymerization procedures involving copolymerizing vinylidene diphosphonic ester, a R2 C═CR2 group where R is a combination of electron donating/electron withdrawing groups, a divinyl to trivinyl crosslinking agent and a porogen in combination with an initiator, such as benzoyl peroxide.

It is still a further object of the invention to provide an improved ion exchange resin and method for removing actinide metal ions in III, IV and VI oxidation states and transition and post transition metals from highly acidic and highly basic waste solutions.

These and other objects of the invention will be made clearer upon reference to the following Detailed Descritpion and appended claims along with the drawings described as follows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the steps in a preferred procedure for the manufacture of Diphonix resin for ion exchange use;

FIG. 2A shows the distribution ratio for Diphonix resin over the HNO3 molarity for a variety of metal ions and FIG. 2B shows a comparison set of plots for a commercial AGMP-50 resin;

Preparation of the ion exchange resin necessitated polymerization of various monomers. Any conventional method of polymerization can be used, including bulk solution, suspension, emulsion and precipitation techniques.

The polymerization of diphosphonic acid groups to form an ion exchange resin was most preferably based on vinylidene diphosphonic acid ("VDPA", hereinafter) and its alkyl/aryl esters. VDPA polymerizes with acrylamide and the esters polymerize with styrene or other R2 C═CR2 monomer where R is a combination of electron donating/withdrawing groups. As illustrated in the flow chart of FIG. 1, a variety of additional copolymerization entities can also be used including: (1) acrylonitrile or other member of the (meth)acrylate family, (2) divinylbenzene or other divinylic or trivinylic crosslinking agent, (3) 2-ethylhexanol or other porogen and (4) an initiator such as benzoyl peroxide or AIBN, azobis(isobutyro) nitrile ("AIBN"). Appropriate and most preferred ranges of weight percent of each component are also shown in FIG. 1 ("parts" of various components hereinafter refers to relative weight units allowing calculation of weight percent). Examples of specific conditions of such copolymerization steps are set forth in the Examples at the end of the Detailed Description. The polymerization can be commenced by use of an initiator, such as K2 S2 O8, or the ones listed in FIG. 1 or even ionic initiators, such as a strong base like NaNH2.

The end product Diphonix resin can be made either microporous or macroporous by the addition of diluents, such as porogens, to the monomer solution. Typical diluents can include, for example, hydrocarbons (such as toluene) and alcohols (such as 2-ethylhexanol, 4-methyl-2 pentanol and octanol) to achieve a target porosity and surface area.

The manufacture of ionic exchange resin beads can be implemented by including another step of preparing an aqueous phase of CaCl2.2H2 O, polyvinyl alcohol and water. A range of preferred relative weights and the most preferred weight of each component are shown in FIG. 1. This aqueous phase is combined with the organic copolymerizable mixture. The combined mixture is charged to a conventional reactor equipped with a thermometer condenser and overhead stirrer. The mixture is heated to 60°-120° C. (primarily depending on the type of initiator used) for eighteen hours and then stirred to give the desired resin particle size, such as 100-300 microns diameter spheres. The mixture and resin particles are then cooled to ambient, the resin particles water washed and then isolated in a water free environment.

Polymerization of VDPA itself leads directly to a resin with ion exchange proeprties. If a VDPA tetraester is polymerized, a hydrolysis step is usually needed for regeneration of the ion exchange sites of the VDPA. For example, hydrolysis can be implemented by treating the resin beads with 0.5-10N (2N preferably) KOH in a dioxane: water mixture of ratio preferably 1:7. The resin/hydrolysis mixture is refluxed for 18 hours, the resin is washed with water and oven dried at 110° C. for 15 hours.

In another preferred form of the invention, an additional processing step further enhances the kinetics of complexation of metal ions by the Diphonix resin. If the resin to be complexed is in an aqueous or similar solution, this step involves increasing the polymer's hydrophilicity, the moisture holding capacity. This can be accomplished by preparing the Diphonix resin with highly polar monomers, such as acrylic acid and benzenesulfonic acid or post functionalizing it with carboxylic acid and sulfonic acid, for example.

In a most preferred embodiment, Diphonix resin beads are contacted with chlorosulfonic acid (or other sulfonating agent) as a 0.1-25% solution (10% most preferred) in ethylene chloride or other solvent. The mixture is stirred at 25° C. and refluxed until sulfonation is complete (about 1 hour). The resin beads are then dried, washed with dioxane or other solvent, contacted with 0.1-50% aqueous NaOH (preferably 20%) for 17 hours and washed with a cycle of water/HCl/water.

Such additional functionalizations create a multifunctional resin in that the diphosphonic acid groups are accompanied by sulfonic acid and/or carboxylic acid groups. Such multifunctional sites allow use of each group for complexing particular metal ions to which the group is sensitive. Such a multifunctional capability should have substantial commercial advantages.

Distribution Ratio Determination

The Diphonix resin is obtained in the hydrogen ion form using the procedures described hereinbefore. In some studies with transition and post-transition metal ions, the Ca2 + ion form of Diphonix is employed. The Ca form of Diphonix, as well as the Ca forms of monophosphonic and AG MP-50 resins, (commercially available from Bio Rad Corp., CA) were prepared by eluting an ion exchange column packed with ion-exchange resins in the H+ form with excess calcium hydroxide solution followed by several displacement volumes of 2M Ca(NO3)2 at pH=9 [pH adjusted with Ca(OH)2 ] and finally by rinsing with ten bed volumes of water to remove the excess Ca salts.

The sorption of a number of radioisotopes and stable elements from various solutions by the resin was measured by contacting a known volume (typically 1.0 mL) of a spiked solution of appropriate concentration with a known weight of resin. Resins were either the H+ form or the Ca2+ form. The ratio of the aqueous phase volume (mL) to the weight of the resin (g) ranged from 20 to 200. This ratio is determined primarily by the need to produce an easily measured decrease in the aqueous activity of concentration by contact with the resin. Although equilibrium is generally reached in under 15-30 minutes, a 2 hour mixing time was normally employed. In the case of Cr(III), 48 hours mixing time was employed.

The mixing of the solid and liquid phases was performed using small magnetic bars rotated at such a speed (about 200 rpm) that the resin was suspended in the aqueous phase. After equilibration, the phases were centrifuged and the aqueous phase withdrawn from the test tube. To ensure that the aqueous phase did not contain any dispersed resin, it was also filtered through Whatman #1 paper after centrifugation.

Weight distribution ratios were calculated from the following equation: ##EQU1## where Ao and As are the aqueous phase radioactivities (counts per minute) or concentrations (measured spectroscopically) before and after equilibration, respectively; W is the weight of resin (g) and V is the aqueous phase volume (mL). The weight of resin (g) used in the calculation of D may be expressed on a dry weight basis (i.e., resin dried in an oven at 100° C.) or a wet weight basis (i.e., resin filtered and air dried). The D measured for air dried resin (referred to as a wet-weight) was converted to the corresponding D for oven dried resin (referred to as a dry-weight) by dividing 0.372. The factor 0.372 corrects for the loss of sorbed water from the resin on oven drying. When the sorption of various elements was measured using the Ca form of the resin, the correction factor was 0.575.

Sorption from Acidic Media-Comparison with Prior Art

FIG. 2 shows a comparison of ion-exchange sorption of Th(IV), U(VI), Pu(IV), Am(III), Fe(III), and Ca(II) (as measured by the distribution ratio) by a commercially available strong acid sulfonate resin Bio-Rad AG MP-50 and Diphonix. All resins were initially in the H+ form. Bio-Rad AG MP-50 is a macroporous Dowex-50 resin. Strong acid sulfonate cation exchange resins are the most widely used cation exchange resins. The Diphonix resin employed was prepared by the procedure described herein. The data in FIG. 2 show that Diphonix retains Th, U, Pu and Fe much more strongly above 1M HNO3 than the AG MP-50 resin. The difference between Diphonix and AG MP-50 regarding the retention of Am is less pronounced than is the case with Th, U, Pu, and Fe; but Diphonixis still significantly superior to the AG MP-50 resin. Calcium, on the other hand, is more poorly retained by Diphonix than by AG MP-50 (see Table 2). However, this property of Diphonix is an advantage because generally one does not wish to retain Ca. Calcium's lower retention by Diphonix indicates that the Ca in, for example, actinide bearing waste solutions would cause less interference than would be the case for AG MP-50.

The superiority of Diphonix in the rention of Th, U, Pu, Am, and Fe and in the rejection of Ca at high HNO3 concentration is shown clearly in Tables 2 and 3. Table 2 compares the dry weight distribution ratios in 5M HNO3 and Table 3 compares the dry weight distribution ratios in 10M HNO3. Two different cation exchange resins were compared with Diphonix, namely, a monophosphonic acid resin, which is substantially similar to resin commercially available under the trade name Chelite®P, and Bio Rad AG MP-50. Dry-weight distribution ratios were used for the comparison because of the variation of water contents of the three air-dried resins.

The data in Tables 2 and 3 show clearly the superiority of Diphonix resin over the monophosphonic and sulfonic resins in the ability to remove U, Pu, Am, and Fe from strong nitric acid.

Table 4 shows a comparison between Diphonix and the monophosphonic acid and sulfonic resin for U, Pu, and Am for 4M NaNO3 -0.1M HNO3. Again the ion-exchanger sorption of U, Pu, and Am on the Diphonix resin is at least ten to one hundred times higher than on the other two resins. The data in Tables 2, 3 and 4 are highly significant because of the large prevailing number of highly acidic and highly salted actinide bearing waste solutions.

Th, U, Pu, Am and Fe may be efficiently desorbed by contacting the resin (or eluting a column containing the resin) with 0.5 to 1.0M 1-hydroxyethane-1,1-diphosphonic acid (Abbrev. HEDPA) solution. The distribution ratios for Th, U, Pu, Am and Fe are <1 in the presence of 1M HEDPA.

Tables 5 and 6 compare the oven dry-weight distribution ratios at pH 5, 6, 7, and 8 for a number of transition and post-transition elements using the Ca form of Diphonix and of AG MP-50. The Ca form of the two resins was used for ion-exchange sorption measurements to compare the ability of the two resins to selectively remove the various metal ions studied with Ca2 + as the counter ion in the resin phase. High selectivity of a given metal ion, e.g. Pb2+, over Ca2+ and Mg2+ is essential in applications dealing with the removal of hazardous metal ions from, e.g., hard water, waste streams, and contaminated groundwater. The retention of Ca2+ and Mg2+ by Diphonix is essentially the same, therefore it is not necessary to measure distribution ratios using both the Ca form and the Mg form of the diphosphonic resin. Therefore, to demonstrate the effectiveness of the Diphonix resin, the Ca2+ form of the resin was used. The buffer employed to adjust the pH was 0.1M ammonium hydroxide/ammonium acetate/acetic acid solutions. Ammonium ion has a retention very similar to sodium and potassium ions on cation exchange resins, therefore NH4+ does not affect the D measurements.

The data in Tables 5 and 6 show that ion-exchange sorption of the Diphonix resin is significantly stronger for every metal ion studied except for Hg and Sn. Even in the case of Hg and Sn, the diphosphonic resin shows strong sorption. The elements listed in Tables 5 and 6 may be desorbed from Diphonix using a 0.5 to 1.0M HEDPA solution or in the case of Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II) Cd(II), Hg(II), Sn(II), and Pb(II) with 2M H2 SO4.

Diphonix is also superior to other commercially available chelating ion-exchange resins. For example, Chelite C, a stryrene-DVB matrix with iminodiacetic acid groups, does not show selectivity for Mn over Ca and metal ions such as Co(II), Ni(II), Zn(II), and Cd(II) are not retained at pH<4. The distribution ratios for these latter four elements are so high at pH 2 to 5 on the Na+ -H+ form of Diphonix that no radiotracer can be detected in the aqueous phase. Chelite N, a cross-linked macroporous polymer with amidoxime groups, will not retain actinides (Th, U, Pu and Am) from acidic media (pH<2) nor retain transition metals like Co, Ni, Zn, and Cd at pHs< 4. Chelite P, a styrene-DVB matrix with aminomethylphosphonic acid groups, is not selective for Mn, Ni, Co, Cd over Ca nor will it retain actinides, e.g. Am(III) from highly acidic and salt media (see Tables 2, 3 and 4).

As a consequence of these substantially improved metal complexing capabilities, Diphonix can strongly retain actinides from highly acidic and highly salted solutions and strongly retain a large number of transition and post-transition metals in the presence of alkali metal (Na. K) and alkaline earth metal (Mg, Ca) salts at pH's>2. These properties indicate a number of applications, including without limitation:

3. Removal of traces of toxic metal such as V, Cr, Mn, Co. Ni, Cu, Zn, Cd, Hg, and Pb from drinking water to ensure potability.

4. Removal of Mn, Co and Ni from oil refinery process waters generated in washing catalysts used for desulfurization operations.

5. Removal of Cr from pickling liquors.

6. Removal of Fe(III) from chelating agents used in boiler descaling operations.

7. Removal of radioisotopes from rad wastes generated in nuclear power plants.

8. Separation of fructose from glucose.

The following non-limiting examples set forth a variety of methods, products and apparatus used in demonstrating the invention set forth in the appended claims.

EXAMPLE 1

An organic phase consisting of 13.5 parts tetraalkyl(aryl) VDPA ester (which may or may not be oligomerized), 9.30 parts styrene, 3.00 parts acrylonitrile, 2.70 parts divinylbenzene (technical grade). and 1.5 parts azobis (isobutyro) nitrile is charged to a reactor equipped with thermometer, condenser, and overhead stirrer. If it is desired to produce beads, then the reactor also contains an aqueous phase consisting of 41.7 parts CaCl2 H2 O in 80 parts aqueous solution also containing 1.5% polyvinyl alcohol (based on the weight of organic phase). The suspension is stirred at 223 rpm for 18 h at 75° C.

The resulting beads, after washing with water, can be hydrolyzed directly to regenerate the ion exchange sites inherent to VDPA. Alternatively, they can be washed by Soxhlet extraction and used as ionic or molecular coordinating agents.

After hydrolysis, the beads can be used as ion exchange resins. Additionally, the phenyl rings in the polymer (when styrene is used as comonomer) can be sulfonated with any sulfonating agent (e.g., sulfuric acid, chlorosulfonic acid, etc.) to produce a polymer with an enhanced microporosity brought about by its increased hydrophilicity. For example, chlorosulfonation requires only 1 h at room temperature for complete reaction of the phenyl rings; subsequent hydrolysis with sodium hydroxide is then required in order to convert the sulfuryl chloride sites into sulfonic acid groups. By doing so, the solids level of the resin drops from approximately 0.60 g dry resin per g wet resin to 0.30 g dry resin per g wet resin. The final phosphorus capacity of the polymer is 1.8 mequiv/g dry resin.

EXAMPLE 2

Bulk polymerization was carried out in a reaction vessel in a conventional, well-known manner by combining tetraalkyl(aryl) VDPA with 0 to 80 wt % divinylbenzene (DVB) and can be carried out with 4 wt % benzoyl peroxide as an initiator and performed at 80° C. over 18 h. Resin made with 10% DVB has a phosphorus capacity of 4.03 mequiv/g, while resin made with 15% DVB has a capacity of 3.81 mequiv/g, and resin made with 20% DVB has a capacity of 3.54 mequiv/g.

EXAMPLE 3

Bulk polymerization and suspension polymerization (using the aqueous phase as above) were carried out with an organic phase consisting of 45 parts tetraalkyl(aryl) VDPA, 23 parts butyl acrylate, 10 parts vinyl propionate, 10 parts technical grade DVB, and 2 parts azobis(isobutyro)nitrile. An additional 25% (based on total monomer weight) of 2-ethylhexyl alcohol was added as porogen. After Polymerization, the porogen is washed free of the polymer with methanol; steam distillation is an alternate method of purification. The polymer has a phosphorus capacity of 2.22 mequiv/g before hydrolysis and 2.95 mequiv/g after hydrolysis with HCl.

EXAMPLE 4

The reactivity of vinyl phosphonic acid (VPA) and its esters is the same as found for VDPA and its esters. In a typical example, 5.11 parts dialkyl VPA, 1.11 parts acrylonitrile, 3.44 parts styrene, 1.09 parts technical grade DVB, and 0.44 parts azobis(isobutyro)nitrile was bulk polymerized at 80° C. for 18 h. The resin has a phosphorus capacity of 1.43 mequiv/g before hydrolysis and 0.94 mequiv/g after sulfonation.

EXAMPLE 5

A copolymerized VDPA was prepared as described in FIG. 1 using the following components: 45% tetraethyl VDPA, 29% styrene, 10% acrylonitrile, 5% divinylbenzene, 3% trimethylolpropane trimethacrylate, 5% benzoyl peroxide. A suspension polymerization was carried out as explained in FIG. 1 with no hydrolysis or sulfonation steps taken. The yield was 65% for polymer and 64.8% of VDPA into the polymer.

EXAMPLE 6

The effect of acrylonitrile on the gel point, polymer yield and VDPA incorporation was determined in a bulk polymerization of monomers.

A first specimen A consisted of 450 mg tetraethyl ester of VDPA, 250 mg of butylacrylate and 250 mg styrene. The gel point was 300 minutes, 44% yield of polymer and 81% of the VDPA was incorporated.

Specimen B consisted of 450 mg tetraethyl ester of VDPA, 100 mg of acrylonitrite and 310 mg of styrene. The gel point was 80 minutes, the polymer yield was 68% and 86% of the VDPA was incorporated.

Specimen C consisted of 300 mg tetramethyl ester of BDPA, 250 mg acrylonitrile and 300 mg styrene. The gel point was 21 minutes, a 71% polymer yield and 65% of the VDPA was incorporated.

All of the three specimens also included 5% divinylbenzene and 5% benzoyl peroxide.

EXAMPLE 7

Polymerization of tetraethyl ester VDPA was carried out using only divinylbenzene as a crosslinking monomer. The full composition of components was 50% tetraethyl ester VDPA, 25% divinylbenzene, 20% ethylvinylbenzene, 5% benzoyl peroxide and 25% ethylhexanol (weight percentages). The preparation was a bulk polymerization performed by the procedure of Example 2. The polymer yield was 54.2%, 85.3% of the VDPA was incorporated into the polymer, and the resulting resin complexed 26.7% of the Eu (III) from a 0.04N HNO3 solution.

EXAMPLE 8

Another variation on the above method and product of Example 7 started with a different component percentage of 41% tetraethyl ester VDPA, 30% divinylbenzene, 24% ethylonyl benzene, 5% benzoyl peroxide and 25% 2-ethylhexanol. The bulk yield was 70.4% polymer, 91.6% of the VDPA was incorporated and 26.4% Eu (III) was complexed from a 0.04N HNO3 solution.

EXAMPLE 9

A set of different bulk polymer were prepared with substantial changes in percentage of components only for the initiator such as benzoyl peroxide. Following the basic procedure for bulk polymerization of Example 2, tetraethyl ester specimen had weights of 0.45 g, butylacrylate of 0.32-0.36 g, divinylbenzene of 0.18 g and benzoyl peroxide varying from 0.05 g to 0.01 g over 5 specimens, it was determined that the percentage yields were as follows:

This example describes the polymerization of a diethyl ester of vinyl (mono) phosphoric acid (VPA). These polymerizations were carried out in the same manner as in Example 2. The various proportional components and results are as follows:

This example concerned the copolymerization of VDPA with N, N'-methylene-bis-acrylamide and acrylamide. It was found that equal amounts of VDPA and bis-acrylamide would polymerize in solutions with potassium persulfate as the initiator to give polymers with phosphorus capacities as high as 1.76 mequiv/g (37% incorporated of VDPA). These polymers were white powders which exhibited large swelling ratios in water. In all cases, the acid capacities were found to be twice the phosphorus capacities. A solid-state 31 p nmr study of one such polymer showed a resonance at 27.5 ppm due to the phosphonic acid sites and a narrow unidentified signal at -2.2 ppm. An attempt to prepare a homopolymer under the same conditions was not successful. All of the VDPA/bis-acrylamide polymers displayed a high affinity for trace levels of Fe(III) at equilibrium.

EXAMPLE 13

Specimens were processed in accordance with Example 9, but the divinylbenzene level was varied. (Bulk polymer at 100° C./18 h.) This data is also illustrated in FIG. 4.

Specimens were processed in accordance with Example 9, but the amounts of Et4 VDPA in the copolymer were changed. The effect on the yield was determined, and the % incorp. remained almost unchanged. (10% DVB, bulk polym'n 100° C./18 h.) The data is shown in FIG. 5.

Specimens were processed in accordance with Example 9, but the reaction time was changed. It was determined to be a minor variable as long as the time is greater than approximately 18 hours. (Reaction temp=70° C.; bulk polym'n). The data is shown in FIG. 7.